The formulations of water-based paints containing mineral loads are made up of an aqueous phase, one or more polymers in an emulsion in the liquid phase known as binders, loads, and/or pigments, a dispersing agent, and admixtures as diverse as surface-active agents, coalescence agents, biocides, anti-foaming agents, and finally, a thickening agent.
This thickening agent makes it possible to control the rheology of the aqueous formulations which it is added to, and particularly water-based paints, both during the stage of their manufacture, and during their transportation, storage, or implementation. The diversity of the practical constraints within each of these steps is due to a variety of different rheological behaviors.
However, the need of the person skilled in the art may be summarized as achieving the effect of thickening the aqueous formulation, both for reasons of stability over time and for a possible application of the paint onto a vertical surface, the absence of splashing at the time of implementation, etc. This is why additives which contribute to this regulation of the rheological behavior have been designated as thickeners.
Among these products, so-called “associative” thickeners are distinguished, which are water-soluble polymers with insoluble hydrophobic groups. Such macromolecules have an associating nature: once added to water, the hydrophobic groups may assemble into micellar aggregates. These aggregates are bound to one another by the hydrophilic parts of the polymers: a three-dimensional network is thereby formed, which causes the medium's viscosity to increase.
The associative thickeners' operating mechanism and characteristics are currently well-known and described, for example, in the documents “Rheology modifiers for water-borne paints” (Surface Coatings Australia, 1985, pp. 6-10) and “Rheological modifiers for water-based paints: the most flexible tools for your formulations” (Eurocoat 97, UATCM, vol. 1, pp 423-442).
Among these associative thickeners, there is the class of HEUR (Hydrophobically modified Ethylene oxide URethane) associative thickeners. They designate copolymer resulting from synthesis between a polyalkylene glycol compound, a polyisocyanate, and a so-called “associative” alkyl or aryl or arylalkyl monomer made up of a hydrophobic terminal group.
These structures are well-known for developing high Brookfield™ viscosities with a low shear gradient (J. of Applied Polymer Science, vol. 58, p 209-230, 1995; Polymeric Mat. Sci. and Engineering, vol. 59, p 1033, 1988; Polymeric Mat. Sci. and Engineering, vol. 61, p 533, 1989; Polymeric Paint Colour Journal, vol. 176, n° 4169, p 459, June 1986). Numerous examples of this are found in the literature, in which is later discussed the choice of the hydrophobic terminal group, which has a major effect on the end polymer's rheological properties.
Within the context of a cosmetics composition, the document EP 1,584,331 discloses a hydrophobic terminal group having 6 to 34 carbon atoms. The document EP 0,905,157 describes branched chains having 2 to 14 carbon atoms, in view of improving the transparency of the paint films produced in the presence of such thickeners. The document WO 02/102868 describes the use of plurystyrylphenols, which make it possible to improve pigment compatibility. In order to specifically increase the Brookfield™ viscosity, the document EP 0,639,595 discloses linear hydrophobic groups having 4 to 36 carbon atoms.
It is currently known that the more carbon atoms are present in the hydrophobic terminal group's chain(s), the greater the viscosity, and particularly the Brookfield™ viscosity with a low shear gradient (see document WO 02/102868 on page 5). Indeed, the size of the hydrophobic groups will affect the size of the micellar aggregates that they cause once in a solution, which is directly related to an increase in viscosity, as described in the document “Rheology modifiers for water-borne paints” (Surface Coatings Australia, 1985, pp. 6-10).
With regard to the prior art, the number of carbon atoms carried by the hydrophobic group in order to achieve “effective” thickening behavior may be numbered as “at least 16” and preferentially “at least 20”. In addition to this years-old technical requirement, an environmental restriction has more recently been added: this is the requirement to have biosourced products, meaning products not derived from fossil fuels. This approach is in keeping with the concepts of green chemistry and sustainable development.